Substituent Effects Control the Self-Association of Molecular Clips in the Crystalline State

We report the X-ray crystal structure of 11 molecular clips and analyze the influence of substituents
(e.g., OMe, Me, and NO2) and their location on the observed crystal packing. Molecular clips 3a and 3b
form tapelike structures in the crystal due to π−π interactions between the aromatic walls. Compounds
3d, 3eC, and 3fC form dimers driven by critical C−H···O interactions and then form tapes driven by
π−π interactions in the crystal. These two building motifs, π−π and C−H···O interactions, can be used
to rationalize the enantio- and diastereoselectivity observed in the X-ray crystal structures of the remaining
five molecular clips. For example, the C−H···O interactions are found to dictate the formation of
homochiral dimers in the structures of (±)-3eT and (±)-3fT and to control the diastereoselective formation
of 6a2−6c2 dimeric motifs with internal p-dimethoxy-o-xylylene walls. Overall, the results suggest that
substituent effects that induce even weak intermolecular interactions (e.g., C−H···O) can be used to
reliably control crystal packing within glycoluril-based systems.